This invention relates to valve mechanisms of the type employed for the control of hydraulic cylinders or other fluid motors, and has more particular reference to the provision of valve mechanism for automatically controlling and coordinating the motions of a number of hydraulically operated work performing members which must be actuated singly and/or in concert in order to effect a desired work cycle.
Front end loaders and backhoes are but two examples of apparatus having work performing members that are hydraulically operated, and whose motions must be coordinated to produce a prescribed work operation. In a front end loader, for instance, it is the boom and the bucket on the outer end of the boom whose motions must be coordinated in order to effect the dig cycle of the loader.
In a backhoe, however, there are three hydraulically actuated work performing members whose motions must be coordinated in order to effect a digging cycle. These are its boom, the dipper stick which is pivotally mounted on the outer end of the boom, and the dipper or bucket which is pivotally mounted on the outer end of the dipper stick.
The operator of a backhoe must be highly skilled in the proper manipulation of conventional control valves which govern the motions of the boom, stick and bucket during digging. At the start of a dig cycle, for example, the operator must actuate the stick cylinder control valve to its "crowd" position so that the stick will force the bucket on its outer end into the ground. He must be able to sense when digging prssures rise to an objectionably high level and at that time "curl" the bucket to a less effective digging attitude to relieve excessive digging pressure. He may, at times, also have to stop the digging or "crowd" motion of the dipper stick by its control valve in order to sufficiently reduce the work load on the stick cylinder. Frequently, as in cases where the bucket strikes an obstruction or encounters extremely compact soil, the operator may have to effect elevation of the boom in order to effect the desired reduction in work load on the hydraulically driven members.
From this it will be seen that there can be times when the operator should be able to continually manipulate the actuating levers of all three control valves governing operation of the hydraulically driven stick, bucket and boom. This is exceedingly difficult, and has greatly limited the operation of backhoes to only those persons having the necessary high degree of skill essential to efficient digging.
Efforts have been made in the past to achieve "automatic dig" for backhoes, to enable their operation by unskilled operators such as might be in the employ of contractors who rent such apparatus. These efforts however, have met with more or less indifferent success. Much of the reason for this resulted from the costly and complicated control mechanism which was needed in order to effect "automatic dig." In some cases, two complete sets of controls were required, one to enable manual control of each work performing member, and the other to effect automatic control of the hydraulic cylinders for the work performing members. The high initial cost and upkeep expense of such a system of automatic dig can be readily appreciated.